1. Field of the Invention
This invention relates to roller door apparatus and more particularly to a roller door apparatus in which a curtain is movable at a high velocity either to or from a closed position in which the curtain extends across a door opening with high tension. The apparatus avoids excessive stresses in the curtain and other components, is very safe and highly reliable in operation and is readily and economically manufacturable.
2. Background of the Prior Art
In a typical type of roller door construction of the prior art, a roller is supported in an elevated position over a door opening and a curtain is unwound from the roller and moved downwardly to a closed position covering the door opening, or is wound back up on the roller to an open position allowing passage through the door opening. To balance the torque applied to the roller from the forces of gravity acting on the curtain, a torsional counterbalance spring within the roller has been used in some constructions. In other constructions, a counterbalance weight has been connected to the roller. It is also known in the art that a tensioning force may be applied to a flexible curtain, using a flexible tensioning member connected to the lower end of the curtain and extending down around a guide pulley and thence upwardly to be wound up on a roller while a curtain is unwound from the roller, and vice versa.
To move a curtain between open and closed positions, hydraulic and electric motors have been controlled by proximity switches to come to a stop at limit positions of movement of the curtain.
These and other roller constructions of the prior art have been generally satisfactory, but have had limitations, particularly with respect to speed with which opening and closing operations are effected, and they have been subject to break-downs and have not otherwise been as reliable and durable as would be desired.